Constraints

A constraint is a restriction set on the start or finish date of a task. Constraints can be flexible (not tied to a specific date) or inflexible (tied to a specific date).

You can specify that a task must start on, or finish no earlier or later than, a particular date.

The Gantt supports all of the common constraint types.

• ASAP As Soon As Possible
• ALAP As Late As Possible
• FNET Finish No Earlier Than
• FNLT Finish No Later Than
• MFO Must Finish On
• MSO Must Start On
• SNET Start No Earlier Than
• SNLT Start No Later Than

The default is As Soon As Possible.

As Soon As Possible (ASAP) (Flexible)

With this constraint, Project schedules the task as early as it can, given other scheduling parameters. No additional date restrictions are put on the task. This is the default constraint for newly created tasks in projects scheduled from the start date.

• Create Two Tasks

• Link the Two Tasks while both have the ASAP constraint 

The start of the second task will be pushed out till after the end of the first.

• Extend the Duration of Task A Using the “Drag” Function.

The start date of Task B will be pushed out.

Must Start On (MSO) (Inflexible)

This constraint indicates the exact date on which a task must be scheduled to begin. Other scheduling parameters such as task dependencies lead or lag time, resource levelling and delay, can't affect scheduling the task unless this requirement is met.

• Create Two Tasks with Different Date ranges. Have Task A with a longer duration than Task B.

• On Task B define the start date by typing in a date before the end of Task A

• On Task B define the constraint as Must Start On

• Link tasks A and B together

• There should be no change in the start date of Task B due to the fact that you have defined the Constraint as MSO.

Note: You can extend the length of the predecessor task (i.e Task A) with no impact on Task B.

Must Finish On (MFO) (Inflexible)

This constraint indicates the exact date on which a task must be scheduled to be completed. Other scheduling parameters such as task dependencies lead or lag time, resource levelling, and delay can't affect scheduling the task unless this requirement is met.

• Create Two Tasks with equal durations. Task B should have a start date after the start date of Task A.

• Link the Two tasks together.

• On Task B define the Must Finish on Constraint.

• Extend the duration of Task A.

Note that there is no change to the end date of task B after the link has taken place.

Note: If you wish to remove an unwanted constraint, select As Soon As Possible (ASAP).